Today's advancements in internal combustion engines have required equal improvements in many component parts. For example, because of the stringent environmental emission government standards, many of the prior art engines required new and improved engine valves that would minimize the amount of oil permitted to enter the valve guide or combustion chamber. At the same time, however, proper lubrication of the valve train and valve wear remain primary concerns for today's advanced engines.
The mating surfaces of the stem of an engine valve in an internal combustion engine presents a wear concern if the metallurgical structure and roughness profile of the stem are such that galling or abrasion between the mating surfaces occurs. As the auto industry has evolved, both engine durability and emission control requirements have placed additional burdens on engine valve finishes.
An early advance in the art was to chrome plate engine valves on a mass production basis. Initially, chrome thickness of 0.00015 to 0.00025 inches with a hardness of Rockwell C 65 was sufficient to prevent galling on the exhaust valve stems of V8 engines. "Galling" is defined as an action approaching cold welding, such action causing adjacent surfaces to have a tendency to stick to each other.
Since that time, the stems of millions of automotive engine valves (particularly exhaust valves) have been plated with hard chrome to minimize galling. The process became more popular in the mid 1970's when emission standards were specified for U.S. automobiles.
When chrome is applied to engine valve stems, it is very hard and resides on the stem surface with microscopic nodules and unevenness. These characteristics can cause valve guide and valve seal wear. In the late 1970's and early 1980's these nodules were identified as the primary cause of valve guide wear and premature engine failure. Chrome nodules were identified as the source of the problem. It was at this time that polishing an engine valve was proposed so that a maximum peak height of the nodules was under 32 Rp micro inches after plating and polishing. This development became the standard industry procedure in the 1980's for eliminating guide wear and/or galling of the valve stem on North American-produced engines.
There have been prior art valves that have been concerned with valve treatment to improve wearability and performance of engine valves. Some of the prior art features are disclosed in U.S. Pat. Nos. 1,569,455 (Burwell); 1,599,172 (Goodbrake); and 3,345,976 (Pope, et al.).
Burwell teaches the use of an annular oil groove 16 which is formed in the upper valve stem portion. The oil groove 16 is normally located just below an asbestos wiper; when the valve is opened, oil will be carried by groove 16 to the asbestos wiper. Groove 16 is in communication with spiral grooves 17 which are provided around the valve stem to a point adjacent to the lower end of the valve guide. Nowhere is Burwell concerned with the surface smoothness of the valves to prevent abrading and wearing. Burwell's objective is merely to lubricate the valve and is not concerned with a long-wearing valve adapted for today's advanced internal combustion engines nor is he concerned with emission problems. Naturally, Burwell's patent in 1926 could not have suggested the problems or solutions for today's complex engine and valve requirements.
Goodbrake (U.S. Pat. No. 1,599,172) also discloses the use of a spiral groove 6 of about one-sixteenth of an inch deep. Again, Goodbrake's invention is concerned with 1926 engine problems and is not directed to 1992 present day high-tech valve-engine concerns or emission standards. At the time of Burwell and Goodbrake's inventions, proper lubrication was believed to be solely responsible for preventing valve wear and galling. Today we know that valve surface imperfections and nodules are primary causes of galling and of seal and valve guide wear. Nowhere does Goodbrake suggest investigating surface smoothness to minimize seal and valve guide wear.
U.S. Pat. No. 3,345,976 (Pope, et al.) shows a valve for an internal combustion engine having an annular longitudinal groove 11b which connects the flats 21 and 20 so that the lubricant flows down one of the flats 20, 21. The flow of lubricant in Pope is greater in volume than would normally occur. The increase volume alledgedly insures frequent change of the lubricant volume located in the annular recess 11b and renewal of lubricant in the flats 20 and 21. Longitudinal grooves such as those suggested by Pope could cause accelerated wear on seals and valve guides as will be later discussed.
With today's strict emission standards for internal combustion engines, none of the lubricating expedients suggested by Burwell, Goodbrake or Pope, et al would suffice. For example, the 1/16 inch groove of Goodbrake would hold far too much oil and would likely cause oil to enter the combustion chamber causing severe emission problems.
Cross hatching of the present invention is far superior in today's engines than the above spiral or longitudinal grooves because of lead-in problems possible with spiral and longitudinal grooves. Additionally, cross hatching aids in low engine idling and cold starting conditions.
Recently, after 1965, engine manufacturers have introduced tighter valve tolerance requirements and introduced new valve seals in an effort to reduce emissions and restrict the flow of excess oil down the valve stem and into the combustion chamber. As these emission standards became more stringent and valve seal design became more sensitive to seal abrasion and seal wear, more advanced methods and technology were researched to produce a mating surface on the valve stem that would provide good wear properties on the valve guide and the seal.
It has been determined that the microscopic texture of the valve stem surface caused the wear and could be reduced to a plateau-like surface and therefore be controlled to support an oil film in the remaining cross hatched micro valleys.